THURSDAY, Jan. 18, 2018 (HealthDay News) -- Chowing down on red meat, white bread and sugar-laden drinks might increase your long-term risk of colon cancer, a new study suggests.
These foods all increase inflammation in your body, and the inflammation they cause is associated with a higher chance of developing colon cancer, according to pooled data from two major health studies.
Basically, what makes for a healthy diet overall also appears to promote a cancer-free colon, said senior researcher Dr. Edward Giovannucci. He is a professor of nutrition and epidemiology at Harvard T.H. Chan School of Public Health in Boston.
"It's consistent with what we already recommend for a healthy diet in general," Giovannucci said. "I see that as good news. We're supporting the current evidence, and not telling people to do something completely different from what they've been told."
Previous studies have linked diet factors with colon cancer, but there's been no clear explanation why that might be, he added.
Giovannucci and his colleagues suspected that inflammation promoted by what a person eats could be at least one way in which diet could influence risk.
It's a reasonable theory, said Dr. Nancy Baxter, a professor of surgery at the University of Toronto and an expert with the American Society of Clinical Oncology.
"We know that chronic inflammation has a lot of negative effects on people, and not just on cancer," Baxter said. "It's not a natural state. It's not natural for us to have ongoing inflammation."
To test this possible connection, the researchers gathered data on more than 121,000 people from two studies -- the Health Professionals Follow-up Study and the Nurses' Health Study -- in which people were followed for a quarter of a century to track potential influences on their health.
Participants filled out food questionnaires every four years. Those questionnaires helped researchers determine a dietary inflammation "score" for each person.
There were 2,699 cases of colorectal cancer that occurred during follow-up. The investigators compared the foods these people ate against the diet of people who didn't develop colon or rectal cancer.
People who ate the most inflammatory foods were 37 percent more likely to develop colon cancer and 70 percent more likely to develop rectal cancer, compared with those who had the lowest inflammation diet score, the findings showed.
Processed meat, red meat, organ meat, refined flour and sugary drinks were among the foods linked most to cancer-related inflammation, Giovannucci said.
On the other hand, he noted, green leafy vegetables, dark yellow vegetables, whole grains, coffee and fruit juice appeared to reduce inflammation.
A person appeared to achieve the greatest anti-inflammatory effect from their healthy diet if they also refrained from alcohol, noted Dr. Wafik El-Deiry, deputy director of Fox Chase Cancer Center in Philadelphia.
There were some odd findings, as well.
For example, pizza was said to reduce inflammation even though it's made up of individual items known to increase inflammation; at the same time, tomatoes cropped up as a cause of inflammation.
According to Baxter, "I don't think anyone should take this and say I can't eat tomatoes but I should eat pizza. I don't even know how that makes sense."
Giovannucci said the study is best viewed as looking at a general pattern of healthy eating.
"Since there are multiple factors, a single one by itself isn't overall that important, but they contribute," Giovannucci said. "If you do everything in the right direction, then you will have a significant impact."
For example, people might drink a lot of coffee, which is a powerful anti-inflammatory beverage, but dull its benefits by loading their mug up with sugar, he said.
"The items add up," Giovannucci explained. "You can't single one thing out."
That's right, said Marjorie McCullough, strategic director of nutritional epidemiology for the American Cancer Society.
"It's important to focus on the overall pro-inflammatory diet, rather than on the specific foods contained in this diet pattern," McCullough said.
"Also, the impact is likely to be even greater, as the foods in this pattern capture only some of the foods that are likely to influence inflammation in the body," McCullough added. "For example, certain spices and food preparation methods are not included, which may have strong effects on inflammation."
Baxter noted that the people with the highest risk of colon cancer were the outliers in the study -- the one-fifth of participants who were consistently eating a lot of foods that promote inflammation.
"These are people who don't have a typical diet," Baxter said.
The study was published online Jan. 18 in the journal JAMA Oncology.
For more on preventing colon cancer, visit the American Cancer Society.